1. Field of the Invention
The present invention relates to a gas turbine airfoil used for a gas turbine.
2. Description of the Related Art
A gas turbine airfoil is exposed on its surface to high-temperature combustion gas. Therefore, the gas turbine airfoil needs to be forcibly cooled in order to inhibit degradation of an airfoil material under a high-temperature condition or lowering of structural strength to ensure its soundness. In recent years, combustion temperature has been increasing to improve the thermal efficiency of a gas turbine. Accordingly, it has been required to forcibly cool also an inner band end wall of a second stage nozzle that has heretofore not been cooled.
One of the documents relating to the present technical field is JP-1993-10102-A. This document describes the fact that “the cooling medium that has cooled the airfoil body (20a) is discharged into a gas path flow. What is important is that the exhaust port (25) of cooling air is provided at a position on the airfoil-leading edge side of the inner band end wall (20b)”. The document further says that “the discharge port (25) is provided at such a position that cooling air is discharged into the cavity (28) defined in cooperation with the bucket (1) located on the upstream side of the nozzle (20)”.
JP-1998-184312-A describes that “the inner band end wall (4b) has the air passage (8) which extends in the circumferential direction and is made to be connected to the inner cooling passage (7) of the nozzle (2b). A jetting port (9) of the air passage (8) is located on the main stream side with respect to the tip of the seal fin (16a) so as to open like a slit.” It is further described that “cooling air is partially passed through the air passage (8) disposed in the inner band end wall (4b) and is continuously jetted from the slit-like jetting port (9) toward the seal fin (16a) of the second stage bucket body (11b) in a circumferential direction. The jetting cooling air is jetted to the sealing device in which the inner band end wall (4b) and the tip of the seal fin (16a) cooperate with each other. At the same time, the jetted cooling air dilutes the gas path flow leaking into the stage gap (25) to lower the temperature in the vicinity of the sealing device”. Incidentally, the symbols shown in the parentheses in the above denote referential numerals and are independent of the referential numerals of the present specification to be described later.